Efficient and effective integrated circuit device heat dissipation during operation is increasingly important as integrated circuit device power consumption continues to rise. This is particularly true for highly integrated devices such as microprocessors and microprocessor chipsets, for example. Ineffective heat dissipation may lead to reliability issues and shorten the useful life of an integrated circuit device.
To prevent such issues, many different types of heat dissipation approaches have been used. For example, system fans, heat pipes and heat sinks coupled to device packages are often provided in an effort to dissipate heat generated by integrated circuit and other electronic devices as quickly as possible. The approach used to dissipate heat for a particular device may depend on the type of package in which the device is provided, the manner in which the device is connected to a system board, and/or the system in which the device will be operating.
Integrated circuit devices, for example, can be provided in many different packages. A particular package may be chosen for a particular integrated circuit device based on many factors including cost, input/output requirements, ease of manufacturing and/or the system in which the package is to be installed. One type of integrated circuit device package is a plastic ball grid array (PBGA) package. A PBGA package may be used, for example, for an integrated circuit device that requires an inexpensive, relatively high input/output count, low profile package.
FIG. 1 shows a cross-sectional view of an integrated circuit device 100 in a PBGA package 102 mounted on a printed circuit board 105. The signal terminals 110 (solder balls for a PBGA package) are electrically coupled to particular traces on the printed circuit board 105 such that the proper signals are supplied to and received from the integrated circuit die 115 within the package 102.
The PBGA package 102 of FIG. 1 also includes several package ground terminals 120 that are provided on the package 102 directly beneath the integrated circuit die 115. The package ground terminals 120 are electrically and thermally coupled to one or more conductive ground layers 125 by vias that extend from a surface of the printed circuit board 105 through the conductive ground layer(s) 125. The package ground terminals 120 provide ground connections for the package 102. The package ground terminals are also provided to dissipate heat from the integrated circuit device 100 into the ground layer(s) 125 of the printed circuit board 105. In this manner, the board 105 acts as a passive heat sink for integrated circuit device 100. The package 102 is referred to as a thermally-enhanced PBGA package because of the manner in which the ground terminals 120 are used.
The above approach, while effective in initially transferring heat away from the die 115, has some disadvantages. The board 105 includes insulating layers 130 on either side of the one or more ground layers 125. The insulating layers 130 are typically formed of fiberglass or another insulating material. While the package ground terminals 120 and conductive ground layer(s) 125 help to transfer heat away from the integrated circuit die 115 into the printed circuit board 105, the insulating layers 130 prevent the transferred heat from being easily dissipated into the ambient. Vias (not shown) across the board 105 provide the only path for the transferred heat to reach the air, but their surface area is insufficient to provide a significant cooling rate.
FIG. 2 is an overhead view of the integrated circuit device 100 of FIG. 1 mounted on the printed circuit board 105 along with other integrated circuit and/or electronic devices 205 and 210. The arrows extending from the perimeter of each of the devices 100, 205 and 210 shows approximate patterns of heat radiation from each device. As shown, the heat conducted away from the die 115 (FIG. 1) and into the ground layer(s) 125 of FIG. 1 may reach other devices 205 and 210, causing the area around such devices to heat up. Similarly, heat transferred from the other devices 205 and 210 to the board 105 may reach the integrated circuit device 100 reducing the effectiveness of the above-described heat dissipation approach.
Another approach is described in U.S. Pat. No. 5,617,294 to Watson et al. ("Watson") which is assigned to the assignee of the present invention. In Watson, a heat slug is installed within an opening in a printed circuit board and an integrated circuit package is attached to a bottom portion of the heat slug such that the heat slug conducts heat away from the integrated circuit package during operation. The heat slug of one embodiment of Watson, however is connected to a ground plane in the printed circuit board such that heat can also be conducted from the integrated circuit package to the ground plane. While the heat slug may be effective in initially conducting heat away from the integrated circuit device, the heat conducted to the ground plane is not easily dissipated.